Industrial ink jet machines for large-scale full color printing with 60 cm to 2 m width have been brought to the market place in recent years. As materials to be printed in these applications, recording materials produced by surface-treating paper or a plastic sheet have dominated in the market. Polyester fabrics are light-weight and flexibility and have high durability and high resistance to tensile tearing and are therefore suitable as base materials for large printing products. These fabrics, however, have irregularities larger than paper or a plastic sheet which have a smooth surface. Hence colorant particles in ink are diffused on the surface of the fabric so that the density on the surface is liable to be seen thin. It is therefore necessary to design a specific ink image receiving layer for fabrics.
While, inks which are used in applications requiring high durability and produced by dispersing a water-insoluble pigment in water are superior durability against wind and rain, UV-rays, NO.sub.x gas and the like but are inferior in print density (OD value) to inks produced by dispersing a water-soluble pigment.
Restrictions on the physical properties and dispersibility of an ink jet ink offer a difficulty in an extreme improvement in ink density. In order to obtain the same density as that of an ink containing a water-soluble pigment by using an ink containing a water-insoluble pigment, it is necessary to make a specific design for the ink using a water-insoluble pigment, which enables an increase in the amount of ink, absorption of the increased ink, prevention of the strike through and development of a high density color on the surface.
The fabric , different from paper and resin sheets, is light-weight, tough, flexibility and elastic. The fabric is very convenient because, putting these physical properties of the fabric, it can be stored and carried while it is folded. However, in a case that the ink image receiving layer lacks in adhesion to the fabric, it readily peels off and falls out, producing whitely faded portions. It is therefore necessary to make specific designs for an ink image receiving layer taking adhesion to a polyester fabric into full consideration.
Development of those limited in feathering by processing an image receiving layer on the print surface of a synthetic fabric is still ongoing these days. However, these fabric products cause insufficient development in color of the ink using a water-insoluble pigment and only a print image giving a dim impression is obtained. Also, the characteristics of the fabric such as feeling, bending characteristics and strength are insufficiently utilized and hence its application is limited.
An examination has been made to form an receiving image layer by using various chemicals to solve these problems.
For instance, an image receiving layer sheet produced by applying a droplet of mixture of a hydrophilic polymer binder and microparticles of silicic acid are disclosed in JP 52-9074A, JP 55-51583A, JP56-148583A, and JP 58-72495A. Since these image receiving layers consist of a porous structure+a hydrophilic resin, they have high ink absorbance and color-developing capability. However, they have insufficient bending characteristics and elasticity and have insufficient water-resistance in particular. Therefore, they are used in applications limited to paper or film materials and applications of these image receiving layers to the polyester fabric are impractical.
An image receiving layer using a basic latex to improve the water-resistance is disclosed in JP 57-36692A. This image receiving layer, though it is superior in the bending characteristic and in the water-resistance, lacks in water-absorption and has inferior color developing capability when a water-insoluble ink is used and also lacks in long-term weatherability.
Image receiving layers in which high water-absorbance acrylic resin particles are dissolved or dispersed, for instance, in a polymer binder are disclosed in JP 57-173294A, JP 57-191084A and JP63-281885A. In the case of a water-type application solution, it absorbs water and is increased in the viscosity when it is prepared, causing its addition to be difficult. Although such a water-type application solution is superior in the ink absorbance and surface color developing capability, it has insufficient water-resistance and poor adhesion to a fabric. Moreover, the high water-absorption resin is liable to hydrolyze viewing from the weatherability and applications of this image receiving layer to a fabric are impractical.
Further, porous image receiving layers comprising pseudo-boehmite which is a coagulant of a boehmite crystal are disclosed in JP 6-184954A, JP 7-238467A, JP 9-104166A and JP 9-123593A. These porous receiving layer exhibits excellent color developing capability when a water-soluble ink is used. However, in the case of using a water-insoluble ink, when it is intended to obtain sufficient surface density by increasing the amount of ink, feathering along a fabric tends to appear from a lack in the ink absorption capability of the image receiving layer and the ink-drying characteristics and the wetting-wear resistance of the composition are also insufficient, limiting applications of the image receiving layer. The image receiving layer has a gas-discoloring tendency and also poses a problem that an offensive odor remains in the layer due to acetic acid used in the production process.
JP 8-2688B discloses that a fabric is coated with a wetting coagulated film of a polymer obtained by reacting a polyisocyanate compound and a polyol. This receiving layer gives a soft feeling peculiar to the wetting coagulated film and has high bending characteristics, elasticity, wear resistance and water-resistance because of a porous structure and high adhesion to a base material when it is applied to a fabric. However, feathering tends to be caused from lack of the water absorption of the resin and is inferior in color development, limiting its applications.
Other than the above disclosures, there is a disclosure of the use of a water-swelling prepolymer produced by masking, with a block agent, a terminal NCO group of a product produced by reacting a polyether polyol with a polyisocyanate as reported in JP 9-216458A. These prepolymers have excellent surface color developing capability and high adhesion to a fabric. However, these prepolymers have insufficient bending characteristics, poor flexibility and inferior abrasion resistance of the dried film. Because these prepolymers have a water-absorbing portion on a primary chain, they are inferior in the water-resistant strength. Also because they are ether-type polyols, they have poor adhesion to a polyester which is a polar base material. Hence they have low peeling strength and are liable to cause a whited phenomenon on account of falling of a resin also in a print image. Further the weatherability and heat-resistance of a final polymer are inferior and the features of the polyester fabric, that is, the fastness of the polyester fabric cannot be utilized sufficiently.
JP 3-42590B discloses the use of a water-swelling reaction polymer of a polyether-type polyisocyanate, JP 9-99635A discloses the use of a self-emulsion type (anionic) reaction polymer of an isocyanate which polymer has a glass transition point of 60.degree. C. or more, and JP 9-150574A discloses the use of a combination of an aqueous polyolefin dispersion solution, an ethylene type copolymer, and a reaction polymer of a polyisocyanate which polymer contains a sulfite as a hydrophilic group. However, these compositions have excellent surface color developing capability, bending characteristics and elasticity but are inferior in the wetting-wear resistance and adhesion to a polyester fabric. Even if these compositions are cross-linked using a usual cross-linking agent, the adhesion is increased but the water-absorbance and density of the compositions is greatly increased and the feathering is increased.
From these problems, conventional compositions are used for base materials, such as paper, white resin sheets and OHP sheets, which do not require long term fastness as long as several years but cannot be used for a polyester fabric requiring long-term fastness. Compositions satisfying the qualities of recording images, adhesion to a polyester fabric and wear resistance (rubbing strength) in a balanced manner are not obtained yet at present when a water-insoluble pigment is used.